Whistlers
Whistlers
Whistlers are produced by lightning. When lightning strikes,
electrical energy flows through the glowing gas that we see as a
lightning flash. This energy is radiated as electromagnetic waves
over a very broad spectrum of frequencies, from very low-frequency
radio waves to visual light. The lowest frequencies are well within
the audio frequency range. Some of these radio waves propagate
upward into the ionized gas (plasma) that exists above
Earth's atmosphere. As the waves propagate through the plasma,
they are guided along Earth's magnetic field, and often echo
back and forth between the northern and southern hemispheres.
The waves travel faster at higher frequencies and slower at lower
frequencies. Therefore, a spacecraft will first detect the
higher frequencies and later the lower frequencies. The result
is a whistling tone, hence the name "whistler."
Space Plasma Wave Research Group
The Department of Physics and Astronomy
The University of Iowa